In existing sprayguns for spraying fluids using conventional atomising air the needle is sealed by woven asbestos filled with a P.T.F.E. (polytetrafluoroethylene) and a grease mixture. Sometimes graphite is used in the grease.
The needles of these existing needle valves are subjected to wear and to improve the seal an adjustment has to be made of a spring loaded collar. This has the disadvantage of having to remove the front of the spraygun to provide access to the needle packing assembly.